"Our mission was a failure," wrote Apollo 13 commander James Lovell, "but I like to think it was a successful failure."

The spacecraft was launched on 11 April 1970, and for two days it looked like the smoothest flight of the Apollo program. Mission control radioed to the astronauts, "We're bored to tears down here."

But about 56 hours into the flight, about 322,000 km (some 200,000 miles) from Earth, one of the two oxygen tanks onboard the service module exploded, causing the other tank to fail as well. The blast blew off a side of the module, and the astronauts lost vital stores of not only oxygen, but also water, propellant and electrical power. In fact, too little power remained to position the service module's rocket engine for an immediate return to Earth. Swigert radioed to mission control, "Houston, we've had a problem here."

Fortunately, there was plenty of reserve oxygen onboard the lunar module, which served as a lifeboat for the astronauts. But they had to take dramatic steps to conserve water and power. "We cut down to six ounces (of water) each per day, a fifth of normal intake, and used fruit juices; we ate hot dogs and other wet-pack foods when we ate at all," Lovell wrote. They all became dehydrated and the crew lost a total of 31.5 pounds (14.3 kg).

"Sleep was almost impossible because of the cold," Lovell wrote. "When we turned off the electrical systems, we lost our source of heat, and the sun streaming in the windows didn't much help. We were as cold as frogs in a frozen pool, especially Jack Swigert, who got his feet wet and didn't have lunar overshoes. It wasn't simply that the temperature dropped to 38 F: the sight of perspiring walls and wet windows made it seem even colder."

But there was an even bigger problem. The carbon dioxide exhaled with every breath needed to be scrubbed from the atmosphere by lithium hydroxide canisters or the astronauts would suffocate. But the lunar module into which they had moved had only enough of the chemical to support two men for two days, and they needed enough to support three men for four days. There was more in the abandoned command module, but the square canisters from the command module (CM) would not fit the round openings in the lunar module (LM). "We would have died of the exhaust from our own lungs if mission control hadn't come up with a marvelous fix," Lovell wrote. "They had thought up a way to attach a CM canister to the LM system by using plastic bags, cardboard and tape -- all materials we had on board. Jack and I put it together: just like building a model airplane."

The remaining problem was how to return to Earth. They were able to use the lunar module's engine to change their trajectory from one that would put them into lunar orbit to one that would take them around the moon and back to Earth. But they needed to fire the engine a second time two hours after rounding the moon to increase their return speed -- and the spacecraft had to be carefully aligned during the burn.

Normally, the astronauts would verify the guidance platform's alignment by sighting a star through the Alignment Optical Telescope. But these weren't normal times. "Traveling with us was a swarm of debris from the ruptured service module," Lovell wrote. "The sunlight glinting on these bits of junk -- I called them false stars -- made it impossible to sight a real star. A genius in mission control came up with the idea of using the sun to check the accuracy of our alignment. No amount of debris could blot out that star! Its large diameter could result in considerable error, but nobody had a better plan. I rotated the spacecraft to the attitude Houston had requested. If our alignment was accurate, the sun would be centered in the sextant." The alignment proved to be less than half a degree off, which was good enough.

Lovell says he was told that the "cheer of the year" went up in mission control. He reports that Flight Director Gerald Griffin (whom Lovell describes as "a man not easily shaken") recalled, "Some years later I went back to the log and looked up that mission. My writing was almost illegible I was so damned nervous. And I remember the exhilaration running through me: My God, that's kind of the last hurdle -- if we can do that, I know we can make it."

The lunar-module lifeboat could not survive re-entry into Earth's atmosphere, so the astronauts had to move back into the command module for the final part of their flight. "The walls, ceiling, floor, wire harnesses, and panels were all covered with droplets of water," Lovell wrote. "We suspected conditions were the same behind the panels. The chances of short circuits caused us apprehension, to say the least. But thanks to the safeguards built into the command module after the disastrous fire in January 1967, no arcing took place."

Four hours before landing, they jettisoned the service module, which had been protecting the heat shield that would keep the command module and astronauts from burning up as they sped down through the atmosphere. "I'm glad we weren't able to see the SM earlier," Lovell wrote. "With one whole panel missing, and wreckage hanging out, it was a sorry mess as it drifted away."

Three hours later, they detached the lunar module and plummeted through the atmosphere. Lovell reports that "it rained inside the CM" as the capsule's deceleration jarred the water droplets from the surfaces on which they had condensed.

Apollo 13 splashed down in the Pacific Ocean on 17 April 1970 at 18:07:41 UT after a mission elapsed time of 142 hrs, 54 mins, 41 secs. The splashdown point was southeast of American Samoa, some 6.5 km (4 mi) from the recovery ship USS Iwo Jima. All three crew members survived.

Command module Odyssey is now at the Kansas Cosmosphere and Space Center in Hutchinson, Kan. Lunar Module Aquarius is presumed to have burned up in Earth's atmosphere. Any surviving parts would have splashed down in the Pacific Ocean northeast of New Zealand.

Apollo 13 astronauts could have died from their own exhaled carbon dioxide. (There was not enough lithium hydroxide canisters to fit the round openings in the lunar module; that is until a quick fix was found.

The lunar-module lifeboat could not survive re-entry into Earth's atmosphere, so the astronauts had to move back into the command module for the final part of their return home.

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David S. McKayDuring the Apollo program, McKay gave the first men to walk on the moon training in geology.